The goal of this research application is to determine the involvement of the estrogen receptors ERalpha and ERbeta in mediating low dose estrogen-induced neuroprotection and the strategy is to study this in a neuronal cell line expressing either ERalpha or ERbeta. Epidemiological studies suggest that estrogen exposure decreases the risk and delays the onset and progression of Alzheimer?s disease, demonstrating the importance of estrogen in brain function. The neuroprotective effects of estrogen are often independent of transcription and protein synthesis, indicating a role for estrogen rapid signaling in mediating the neuroprotective effects of the hormone. At present, it is unclear whether the neuroprotective effects of estrogen are entirely manifested via ERalpha and/or ERbeta. Three specific aims will be used to characterize the mechanism of estrogen-mediated neuroprotection in a neuronal cell line. Aim 1 will use a pharmacological approach to determine the involvement of ERalpha and ERbeta in mediating neuroprotection using an ER-negative hippocampal-derived cell line that stably expresses ERalpha or ERbeta. Biochemical approaches will be used in aim 2 to determine if rapid intracellular signaling pathways such as MAPK, PI3-K, PKC and/or PKA are activated by estrogen to produce neuroprotection in these cells. As many intracellular signaling pathways are activated following activation of a Galpha protein at the plasma membrane, aim 3 will determine if estrogen is acting through Galphai/o, Galphas or Galphaq proteins to confer rapid signaling and/or neuroprotection. It is critical to understand the mechanism of estrogen-induced neuroprotection in order to determine the importance of estrogen replacement therapy in the prevention of neurodegenerative diseases.